The present invention relates to a new type of multilayer textile article which can be used for the production of laminated materials; it also relates to a method and a device for producing material of this kind.
Laminated materials have been known for a very long time and consist of alternately disposed layers of textile material (cloths, nonwoven sheets, etc.) which are impregnated with resin, an assembly of the layers then being heat-treated in order to cause the resin to polymerize and the assembly to become hard.
These materials have been used in numerous applications, either in the form of planar components (plates) or defined by a surface of revolution, with a rectilinear or other generatrix, such as a tube, cone, etc.
So far, various types of multilayer textile structures have been proposed for producing such materials. Among these structures, the one which exhibits the best mechanical characteristics, a very good impact strength and abrasion resistance comprises threads oriented in three different directions, generally perpendicular to each other. Such textile articles are generally referred to by the term "three-dimensional cloths", a term which will be used in the description which follows.
Such three-dimensional cloths may be produced by various processes, the most widely used ones consisting of first forming a two-directional structure by successively stacking either sheets consisting of parallel threads, or woven cloths. The sheets are superposed cross-wise to one another so as to produce good mechanical characteristics in all directions, the third direction being obtained by stitching the superposed sheets in a direction which is perpendicular or oblique to the direction in which the sheets are superposed.
While a method of interconnecting the sheets by stitching to provide threads extending in the third direction of the three-dimensional cloth can be easily employed when the planar articles are to be produced, such a method cannot be easily employed in the manufacture of three-dimensional cloth articles having the shape of a body of revolution, for example cylindrical articles, conical articles, etc.
Various methods of producing such articles have been proposed.
One of these methods is the subject of U.S. Pat. No. 4,080,915 and which, in general, consists of forming, around a support mandrel having a shape corresponding to that of the article to be produced, a superposition of first sheets comprising longitudinal threads extending in a first direction and second sheets comprising parallel circumferential transverse threads extending in a direction which is different from that in which the longitudinal threads in the first series of sheets extend, the superposition being preferably produced by alternately disposing the first and the second sheets. The stack of sheets are interconnected by a third series of threads known as radial threads consisting of parallel stitchings at uniform distances from each other, and generally arranged along the generatrices of the article. For its implementation, a method of this kind requires a complex apparatus, particularly with respect to the construction of the support mandrels, which must be designed so as to be capable of having gaps defined on their surfaces that are sufficient for allowing the passage of a needle during the stitching operation to produce the threads extending in the third direction. When parallel stitchings are produced, the support mandrel has to be rotated stepwise and, each time, a gap must be present below the knitting head. It will be readily understood, therefore, that in this method it is not possible to vary the density of the stitchings readily, since their separation distance is generally uniform.
In addition, in this method, it is virtually out of the question to produce elementary layers of the stack by using two-directional cloths.
To solve this problem of the complexity of the support mandrel, it has been proposed, in U.S. Pat. No. 4,059,468, to dispose a stack of sheets (consisting of parallel threads or of two-dimensional cloths) on a support made of pyrolysable material, and then to stitch the stack of said sheets and the support in the third direction with thread. The support is then removed by heat treatment. A process of this kind overcomes the problems presented by the use of a support mandrel which has gaps as in U.S. Pat. No. 4,080,915, but, on the other hand, the stitchings still extend parallel to the generatrices. Furthermore, the execution of the stitching is complicated since certain precautions need to be taken in order to ensure that the stitched threads interlock within the thickness of the support if loops are not to be formed within the article after the removal of said support by pyrolysis.